1. Field of the Invention
The present invention relates to a heat exchanger using micro-channel tubes, and more particularly to a structure of a heat exchanger using micro-channel tubes, which is applied to an evaporator of a household air conditioner.
2. Description of the Related Art
Generally, a heat exchanger using micro-channel tubes is a heat exchanger, in which refrigerant flows along a plurality of tubes having a diameter of less than several mm. Such a heat exchanger is widely used by a condenser of a vehicle air conditioner.
Korean Patent Publication No. 1996-0009342 discloses a structure of a heat exchanger using micro-channel tubes. Hereinafter, with reference to FIG. 1, the heat exchanger using micro-channel tubes will be described.
The heat exchanger using the micro-channel tubes comprises a plurality of tubes 1 laid in a horizontal direction. The tubes 1 are vertically arranged, and corrugated pins 2 are interposed between the tubes 1. Headers 3 and 4 for distributing refrigerant into the tubes 1 or for collecting the refrigerant from the tubes 1 are placed at both ends of the tubes 1. The headers 3 and 4 are made of an aluminum rod member having a circular cross-section, and placed perpendicularly at both ends of the tubes 1. The tubes 1 communicate with the headers 3 and 4, and separators 10 and 11 for dividing the tubes 1 into several channel groups A, B, and C are installed in the headers 3 and 4.
The plural tubes 1 are divided into an inlet-side channel group A, through which the refrigerant enters to the evaporator, an outlet-side channel group C, through which the refrigerant is discharged from the evaporator, and an intermediate channel group B.
With reference to FIG. 2, the overall flow of the refrigerant in the heat exchanger is described. The refrigerant flows along all of the tubes 1 of each of the channel groups A, B, and C in one direction, and then flows along the tubes 1 of the next groups B and C. That is, the refrigerant, having entered into the tubes 1 through a refrigerant inlet 6, is uniformly distributed into all of the tubes 1 of the inlet-side channel group A, and flows toward the upper portion of the right header 4 above the separator 11. In the upper portion of the right header 4 above the separator 11, the inlet-side channel group A and the intermediate channel group B communicate with each other, the entered refrigerant flows toward the intermediate channel group B and is transmitted to the lower portion of the left header 3 below the separator 10. Then, the refrigerant, having been transmitted to the left header 3 through the intermediate channel group B, enters into the lower portion of the right header 4 below the separator 11 through the outlet-side channel group C, and is discharged to the outside through a refrigerant outlet 8.
Here, non-described reference numerals 7 and 9 represent caps for closing the ends of the headers 3 and 4, and non-described reference numerals 13 and 14 represent side plates placed on the outer surfaces of the outermost corrugated pins 2.
In the above-described heat exchanger using micro-channel tubes, the refrigerant in a gaseous state, having entered into the heat exchanger through the refrigerant inlet 6, flows in each of the tubes 1 from the inlet-side channel group A to the outlet-side channel group C, exchanges heat with air in the tubes 1 to be condensed to a liquid state, and the refrigerant in the liquid state is discharged to the outside through the refrigerant outlet 8.
The heat exchanger using micro-channel tubes is called various names, i.e., an aluminum heat exchanger due to the material thereof, a flat tube-type heat exchanger due to the shapes of the tubes thereof, and a PFC (parallel flow condenser) due to the flow of the refrigerant.
The heat exchanger using micro-channel tubes is advantageous in that it has heat transfer efficiency higher than that of a pin tube-type heat exchanger, thereby being miniaturized. However, the heat exchanger using micro-channel tubes cannot be used as an evaporator of a household air conditioner due to several problems, as follows.
Since the evaporator exchanges heat with air of a high temperature rather than air of the temperature thereof, moisture in air is condensed and condensation of water occurs on the surface of the evaporator. In the conventional heat exchanger using micro-channel tubes, which comprises the tubes laid in the horizontal direction, the condensed water formed on the surface of the heat exchanger is gathered in hollow portions of the corrugated pins between the tubes, thus decreasing heat exchanging efficiency.
While the speed of flow of air around the vehicle condenser is comparatively rapid, such as 3˜4 m/s, the speed of flow of air around the evaporator of the household air conditioner is comparatively slow, such as 0.5˜1.5 m/s, thus reducing a heat transfer rate per unit hour. Accordingly, the conventional heat exchanger using micro-channel tubes requires a large heat transfer area.
While the flow of the refrigerant, flowing in the heat exchanger, from the entrance of the refrigerant into the upper portion of one header to the discharge of the refrigerant from the lower portion of the other header, has an S shape, the refrigerant, flowing in the condenser, is condensed from a gaseous state to a liquid state, thus naturally having an S-shaped flow. As shown in FIG. 2, the number of the tubes 1 of the outlet-side channel group C is smaller than the number of the tubes of the inlet-side channel group A due to the phase change of the refrigerant, thus minimizing pressure loss in the heat exchanger. However, since the refrigerant flowing in the evaporator is vaporized from the liquid state to the gaseous state, it is difficult to apply the channel structure of the condenser to the evaporator.
In spite of the above problems, several methods have been proposed for applying the heat exchanger using micro-channel tubes to an evaporator of a household air conditioner.
Korean Patent Laid-open No. 2003-0063980 discloses a heat exchanger, in which headers are erected horizontally and micro-channel tubes are laid perpendicularly between the headers. Drain holes and line grooves for facilitating the discharge of condensed water are formed in the heat exchanger. Korean Patent Laid-open Nos. 2004-0017447, 2004-0017449, 2004-0017920, and 2004-0019628 disclose structures of heat exchangers for facilitating the discharge of condensed water under the condition that headers and micro-channel tubes are disposed in the same manner as that of the preceding Patent.
As disclosed by the above Patents, an evaporator, in which the headers are erected horizontally and the micro-channel tubes are laid perpendicularly between the headers, can discharge a sufficient quantity of the condensed water, but has disadvantages, such as a small heat transfer area and a difficulty in achieving uniform flow of the refrigerant.
Since the refrigerant at an inlet of the evaporator is in a two-phase state, the refrigerant, which enters into the header of the evaporator, cannot be uniformly distributed to the respective tubes due to the difference of speeds of flow between the gaseous phase and the liquid phase. Particularly, the transmission of the refrigerant from one channel group to another channel group is performed in one header, thus accelerating the above problems.